1. Field of the Invention
This invention pertains to fastening apparatus, and more particularly to apparatus for sonically welding metals.
2. Description of the Prior Art
Ultrasonic welding is gaining widespread acceptance as a method for joining metals. The magazine article "Joining Metals with Ultra-Sonic Welding," Machine Design, Sept. 20, 1984, gives an explanation of ultra-sonic welding, as well as its advantages and disadvantages relative to other types of metal fastening methods.
The joining of insulated electrical conductors is a particularly apt application for ultrasonic welding. As a result, ultra-sonic welding machines have been designed specifically to weld insulated conductors. The machines typically include a pair of anvils that form a work station for the wires to be welded. A front anvil is usually adjustable horizontally with respect to a rear anvil, thus permitting the machine to accommodate different size conductors. A vertically reciprocable tip engages the wires placed between the anvils and applies the sonic energy. The prior tip faces that contact the wires normally have saw-tooth contours.
Despite enjoying a certain degree of commercial acceptance, the prior ultra-sonic welding machines possess certain disadvantages. Front anvil adjustability in prior machines has been accomplished by a screw that protrudes toward the machine operator. The operator must bring the wires to be joined up and around the screw to prevent catching the wire ends on the screw. That is an inefficient operation that requires extra time, motion, and care. In prior machines, the rear anvils are not adjustable. Consequently, it is not always possible to position the wires to be welded at the optimum location under the tip. In addition, with a non-adjustable rear anvil, the pressure exerted by a welded workpiece on the anvils may be so great that it is very difficult to remove the welded workpieces from the anvils. Another disadvantage of prior ultra-sonic welding machine tips is that the saw-tooth designs can cause fracture points in the outer welded nugget surface, which can degrade peel test performance. The design of certain aspects of prior ultra-sonic welding machines also renders them undesirably expensive.
Thus, a need exists for an inexpensive ultrasonic welding machine that joins insulated conductors in a more efficient manner than was heretofore possible.